1. Field of the Invention
The present invention relates to a semiconductor device having MISFETs and a method for manufacturing the semiconductor device.
2. Related Art
“Silicon large-scale integrated circuit” is one of the fundamental device technologies that will support the advanced information society in the future. To achieve high performances from integrated circuits, it is necessary to produce highly sophisticated semiconductor elements such as MISFETs (Metal-Insulator-Semiconductor Field Effect Transistors) and CMISFETs (Complementary MISFETs) that serve as the components of the integrated circuits. Conventionally, the sophistication of devices has been achieved by the scaling rule. In recent years, however, it is difficult to achieve high performances by making devices smaller, due to various physical limitations.
For example, with gate electrodes formed with silicon, there have been problems that the gate parasitic resistance becomes higher as the device operation speed increases, the effective insulating film capacitance becomes smaller due to carrier depletion caused in the interface with each insulating film, and the threshold voltage varies due to penetration of impurities into the channel region.
There have been so-called metal gate techniques by which a metal material in place of silicon is used for the gate electrode. By the metal gate techniques, the gate parasitic resistance can be made lower, the carrier depletion can be restrained, and the penetration of impurities can be restrained. As those effects can be simultaneously achieved, the MISFET performance is dramatically improved.
One of the metal gate techniques is the full-silicide gate electrode technique (hereinafter referred to as the FUSI technique) by which the entire gate electrode made of silicon is silicided with Ni or the like. By the FUSI technique, after the source/drain regions and the likes of a transistor are formed through the same procedures as those of the conventional silicon gate technique, all the silicon is turned into silicide so as to obtain the function of a metal gate. Therefore, the FUSI technique is considered to be a very practical metal gate technique.
Meanwhile, SiO2, which has been used as the gate insulating film material, is recently considered to become unable to satisfy the demand for thinner films. Therefore, there is a technique by which nitrogen is added to SiO2 so as to increase the relative permittivity and reduce the leakage current. In short, by this technique, SiON is used as the gate insulating film. With such a gate insulating film, a more sophisticated CMISFET is realized. Further, employment of a gate insulating film made of a so-called high-k material that has higher relative permittivity than SiON is being considered. For such a high-k gate insulating film, materials such as HfO2 and HfSiON are considered to be practical.
For future CMISFETs, combining the FUSI technique and the SiON or high-k gate insulating film technique is essential. By combining those two techniques, future LSIs that can operate at high speeds and consume less power can be realized.
The FUSI technique using nickel is the most practical (hereinafter referred to as the Ni-FUSI technique). In a case where CMISs are formed by combining the Ni-FUSI technique with a practical high-k gate insulating film such as a SiON film, a HfO2 film, or a HfSiON film, the threshold voltage Vth is set at a low value. Therefore, the work function of Ni-FUSI needs to be adjusted to values suitable for the n-channel MIS transistor and the p-channel MIS transistor, respectively. The most popular technique is the technique of modulating the Ni-FUSI composition and the Ni/Si ratio (the composition modulating Ni-FUSI technique, disclosed by K. Takahashi et al., “Dual Workfunction Ni-Silicide/HfSiON Gate Stacks by Phase-Controlled Full-Silicidation (PC-FUSI) Technique for 45 nm-node LSTP and LOP Devices”, 2004 IEDM, p.p. 91-94, for example). By this technique, the Ni-FUSI of the n-channel MIS transistor is made rich in silicon, and the Ni-FUSI of the p-channel MIS transistor is made rich in nickel. With this arrangement, the threshold voltage Vth of each CMIS can be easily adjusted.
However, the biggest problem in the composition modulating Ni-FUSI technique is that a high-temperature process is required as the solid phase reaction temperature for the silicon-rich NiSi2 required for the n-channel MIS transistor is 650° C. or higher. Since the nickel silicide is formed after the source/drain portions of the transistor are formed by the Ni-FUSI technique, the silicide forming temperature needs to be so low as not to degrade the electrode silicides of the source and drain or the impurity profile in the channel. A process at the temperature of 650° C. does not satisfy this requirement.
As a technique for forming the Ni-FUSI of the n-channel MIS transistor at a low temperature, there is the Ni—Al silicidation technique by which a solid phase reaction is caused between silicon and a mixed film of nickel and aluminum, so as to segregate aluminum in the interface between nickel silicide and the gate insulating film that is a HfO2 film in this case. By this technique, a low work function suitable for adjusting the threshold voltage Vth of the n-channel MIS transistor can be realized (see Y. H. Kim et al., “Systematic Study of Workfunction Engineering and Scavenging Effect Using NiSi Alloy FUSI Metal Gates with Advanced Gate Stacks”, 2005 IEDM, p.p. 657-660, for example). By this technique, the Ni-FUSI of the n-channel MIS transistor can be formed at a low temperature that is allowable in practice. By the Ni—Al silicidation technique, however, there is the need to form a Ni—Al alloy only on the n-channel MIS transistor, resulting in more complicated manufacturing procedures.
As described above, there has been the problem that the processing temperature is too high to reduce the threshold voltage Vth of the CMIS transistors forming the Ni-FUSI/SiON or high-k gate insulating film structure by the composition modulating Ni-FUSI technique that is the most popular technique, where a lower threshold voltage Vth is necessary to produce future high-speed semiconductors that consume less power. There also has been the problem that the manufacturing procedures become more complicated by the Ni—Al silicidation technique.